This invention relates to an improved fiber optic connector of simple structure having low connection losses when employed with fiber optic cable. The invention also relates to a tool for assembly such a fiber optic connector and a method of using the tool to assemble the connector. More specifically, this invention relates to such a connector for use with both single and multi-mode fibers, but the preferred embodiment finds special use with multi-mode fiber optic cables resulting in a very low loss connector of the type generally known as an SMA ceramic ferrule connector.
The use of optical fibers as a means for transmitting optical signals in the field of optical communications has been known for many years. When employed in such systems, it is necessary to interconnect different fibers within the system to complete the communications link. However, in such connections it is often found that not only are there transmission losses when the light is transmitted through the optical fibers, but extensive transmission losses also result from the actual fiber connections themselves. In order to eliminate or minimize such interconnection losses, fiber alignment must be achieved with accuracy on the order of microns, and at the same time the fibers have to closely abut in a manner such as to not damage the cleaved or polished fiber ends.
One prior approach to centering fibers or wave guides within aligned connectors is disclosed in U.S. Pat. No. 4,440,469 to Schumaker. The device of Schumaker is an SMA-style optical waveguide connector, the type to which this invention is directed, and includes a tubular contact body having an axial passageway profiled for receiving a primary ferrule therein. The passageway is further profiled for retaining the primary ferrule at a rearward location, which ferrule receives an optical waveguide therethrough with a forward end segment of the waveguide extending forward from a forward end of the contact body. An alignment ferrule is provided and is mounted over the forward end of the contact body and received on a forward segment of the optical waveguide. The forward end of the primary ferrule and the inner profile of the contact body passageway are structured to interfit and define a region wherein adhesive material is inserted from the forward terminal end of the connector assembly. The adhesive is retained within this region by the alignment ferrule which fits over the forward segment of the optical waveguide.
Although intially aligning the fiber precisely, as the adhesive sets, some shrinkage of the adhesive occurs in the device of Schumaker, and it is not possible to achieve fine fiber alignment readily and reliably with such an arrangement. Moreover, the use of the adhesive complicates the assembly operation and requires long setting times and often, due to the setting of the adhesive, even if misalignment does not occur, changes in temperature will cause shrinkage or expansion of the adhesive ultimately resulting in creation of a gap and in the fiber ends being moved out of abutment with each other.
An alternative approach to solving these problems is disclosed in U.S. Pat. No. 4,487,474 which teaches the use of a pair of ceramic optical plugs having optical fibers extending coaxially therethrough which fit within a ceramic sleeve. A coupling nut serves to hold the two plugs together to effect the interconnection between the optical fibers. Although generally providing improved results over the adhesive employing prior art system described above, the connector of said patent includes disadvantages in that it is difficult to ensure that the two ceramic plugs are tightly held against each other.
One advantageous embodiment of a connector which avoids the above-discussed disadvantages is disclosed in copending U.S. Application Ser. No. 766,743 which was filed Aug. 16, 1985, and which has inventors in common with those of this application. The connector described therein is generally satisfactory but it is complicated in construction and it is preferred for use with single mode fibers where the question of losses become even more critical than when multi-mode fibers are concerned.
A more preferred SMA type connector is described in a product brochure by Ofti dated Nov. 28, 1984 discussing epoxy style-SMA ceramic series FO connectors. The connector described therein comprises typically a main body having a coupling nut attached thereto and in the front a ceramic ferrule receiving recess. In such connector the cable is mounted within the connector in a conventional manner. The fiber is passed through a ceramic ferrule at the end, which ferrule is epoxied to the main housing in the recess, with the fiber being epoxied within the ferrule. The tip of the fiber extending from the ferrule is cut to a point where it extends beyond the end of the connector. Thereafter, the ceramic and the fiber are conventially ground and polished down in size to a desired length for both the ceramic as well as the fiber. While providing satisfactory results generally for use with both multi-mode and single mode fibers, the assembly of such a connector is difficult and further, ensuring the proper length for the ceramic also becomes difficult since it is a time consuming process and always not possible to maintain tolerances in the manufacture of the main metal body, and thereafter in the polishing operation, since variations in polishing techniques will affect the end face of the ceramic either in that it will be too short, too long or the end face will at an angle thereby creating an angular misalignment situation with respect to fibers being interconnected.
It is thus according to the invention that such a ceramic type connector is provided which is of simple construction and it is easily repeatable in terms of construction to provide connectors having extremely low losses.